Why Light Attracts Insects!
Written and verified by the biologist Cesar Paul Gonzalez Gonzalez
When you switch on a light bulb at night, you’ll usually find a great variety of insects come and fly incessantly around the light. This is a common and very annoying situation with flying arthropods (especially dipteran and lepidopteran insects). Find out why light attracts insects in this article.
The truth here is that the insects are completely confused and this is the reason why they keep circling round and round. The simple act of turning on a light bulb in the middle of the night has an impact on these insects’ perception. Keep reading and we’ll tell you exactly why light attracts insects.
Insect vision
Insect eyes are very different from those of other animals, as they aren’t able to perceive the same colors and intensity of light. This is because they contain different photoreceptors, which are responsible for “interpreting” lighting. For this reason, they react to stimuli that humans don’t perceive well, such as UV and infrared light.
The two types of visual structures that most insects have are ocelli and compound eyes. Both can perceive light intensity, but only the latter is able to obtain the sharper images that help them make decisions. This is called phototaxis, which is the ability of insects to respond to light.
Arthropods react by natural “instinct” to any type of lighting. The key point is the action they are “programmed” to take in response to these stimuli. In general, their behavioral pattern is divided into two: flight (negative phototaxis) or attraction (positive phototaxis).
Why is phototaxis important?
Light is a valuable indicator for insects, as its presence or absence helps them to identify the conditions of their environment. For example, cockroaches are “afraid” of light because it helps their predators find them – that’s why they hide and come out only in the dark. This negative phototaxis allows them to identify danger in order to avoid it.
On the opposite side are bees, which are characterized by going from flower to flower and feeding on nectar or pollen. Although it may seem that this search is random, they’re actually attracted by the reflection of UV light emitted by certain flowers. In this way, positive phototaxis allows them to save time and easily reach the plants that contain their delicious food.
Why light attracts insects
Light attracts nocturnal insects to a greater extent. However, not all of them exhibit positive phototaxis, as each has a different way of interpreting the light stimulus. Some of the reasons why these organisms seek a source of illumination are as follows:
- Orientation: Moonlight helps them to orient themselves and artificial lighting confuses them.
- Guidance for obstacle avoidance: Intense illumination indicates that the flight area is clear (no obstacles).
- Communication: For bioluminescent insects, such as fireflies, light serves as a means of communication between them.
We’re now going to look at each of these phenomena in a little more detail. Don’t miss it!
The moon as orientation
Their biological development process led to nocturnal insects being guided by the light of the moon. In former times, this was the only natural object that illuminated the nights. For this reason, the introduction of artificial light confuses them, as they haven’t adapted ways of distinguishing between the two types of illumination.
This problem is worse if we take into account that an arthropod’s vision isn’t very sharp.
Clear skies
For some insects, the moonlight allows them to identify whether the path is clear or not. This interpretation is simple: the more light there is, the fewer obstacles there are to avoid. The problem arises when a second light source makes the insect believe that there’s a clear flight path, which makes it feel attracted to the light bulb.
Bioluminescent insects
In bioluminescent insects, light plays a major role in their communication. This causes the organisms to be very confused by artificial light sources. For example, in the case of the common European firefly (Lampyris noctiluca), males seek out females by means of their brightness. This characteristic causes them to be attracted to light bulbs.
The impact of artificial light on insects
Artificial light attracts insects in the same way that natural light (the moon) does. This means that cities have a great impact on the lives of these organisms. At the same time, it condemns them to a slow death by burning their wings. Not only are people inconvenienced by them, but several species are being driven to the brink of extinction.
One possible solution is to use warm lights that produce a low amount of UV light. Although this doesn’t completely prevent the insects from being attracted to them, it considerably reduces the negative effects the light has on them. In addition, solving this conflict also requires a change in people’s habits, as the excessive consumption of light energy often becomes a normal part of our lives.
This problem is also called light pollution and can be defined as the excess of artificial light during the night. This causes various physiological imbalances in wild species and even affects human health. If you want to help to reduce the problem, try to turn off unnecessary lights at home, and close the windows, especially at night.
All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.
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This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.